Low-methoxyl pectin was extracted from sunflower heads and
head-stalk mixtures (1:1, w/w) and modified either during or after
isolation, by NH4OH demethylation. The number of processing steps
was reduced substantially by modification during pectin isolation.
The poor gelation characteristics of native sunflower pectins
(pregelation, brittleness and lack of elasticity) were improved by
NH4OH demethylation, especially with head pectins. The NH4OH
treatments were effective in reducing the methoxyl, acetyl, and
ash contents, and molecular weight, and in increasing the acid
amide and galacturonic acid contents. It was presumed that the
improved gelation characteristics were related to these changes in
chemical composition, and to greater randomization of methoxyl and
carboxyl groups along the polygalaturonic acid chains.
For demethylation of rehydrated pectins, a high demethylation
rate and high amidation efficiency were associated with a high
degree of hydration of pectin particles, high NH4OH concentrations,
and low temperature. For demethylation of pectin extracts and
pectin precipitates, a high demethylation rate and high amidation
efficiency were again associated with high concentrations of NH4OH
and low temperature. The extent of demethylation and amidation
were dependent upon reaction time, NH4OH concentration, and
temperature. Reductions in molecular weight proceeded at a slower
rate at higher concentrations of NH4OH and a low reaction temperature.
A pH of 4.3 was optimal for gel formation in the case of pectins
(head and head-stalk mixtures) from the 1976 sunflower crop, which
contrasted with a value of 3.0 for pectins isolated from 1977
sunflower heads.
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